WO2019034450A1

WO2019034450A1 - Heat exchanger

Info

Publication number: WO2019034450A1
Application number: PCT/EP2018/071098
Authority: WO
Inventors: Sebastian Unger; Uwe Hampel
Original assignee: Helmholtz-Zentrum Dresden - Rossendorf E. V.; Technische Universität Dresden
Priority date: 2017-08-16
Filing date: 2018-08-03
Publication date: 2019-02-21
Also published as: EP3669133B1; EP3669133A1; JP2020531774A; US20210131747A1; DE102017214261A1

Abstract

The invention relates to a heat exchanger having at least one partition and surface elements which project from at least one side of the partition and which enlarge the surface of the partition and around which a fluid can flow. The problem addressed by the present invention is that of proposing heat exchangers of low mass with high thermal transmission capacity. This problem is solved by means of a heat exchanger in which the surface elements are formed so as to project in the manner of fins from the partition, and the surface elements have reinforcement beads, wherein the reinforcement beads extend as far as the partition.

Description

Heat exchanger

The present invention relates to a heat exchanger with at least one partition wall, from which surface elements projecting on at least one side are arranged, which can be flowed around by a fluid.

Heat exchangers are used in the prior art in various embodiments for the transfer of heat from one medium to another medium, the two media remain physically separate. According to the type of media, which are also referred to as fluids, one can subdivide heat exchangers, for example, in liquid-gas heat exchangers, liquid-liquid heat exchangers and in gas-gas heat exchangers. In the field of liquid-gas heat exchangers tube bundle heat exchanger with finned tubes are known, which are also referred to as finned tube heat exchanger. The liquid flows inside the tube and the gas flows around the tube on the outside. The heat transfer coefficients of liquids are hereby one to two orders of magnitude larger than with gases. The surface of the tube is therefore externally enlarged by ribs whereby a reduced heat transfer resistance is present on the gas side of this heat exchanger. As a result, the heat transfer resistance for both media are small. The fins of finned tubes are often designed in the art as bulky lugs, which are connected to the partition wall of the heat exchanger. Large volumes of the ribs are coupled with high material costs in the manufacture and a large weight of the heat exchanger. High weights can be detrimental and undesirable, for example when used in vehicles. A high material consumption is disadvantageously associated with correspondingly high costs. A large wall thickness of the individual ribs, referred to below as rib thickness, leads to a lower number of ribs per rib tube with the same distance between the ribs than with thinner ribs. With a large rib thickness, limited heat transfer surfaces and low overall thermal performance are associated.

The document GB 436,656 discloses heat exchangers with finned tubes, in which the ribs in the form of three-dimensionally configured surface elements have an enlarged surface. A disadvantage of these finned tubes is the mass increase, which is proportional to the volume of the three-dimensional structures and a limited overall thermal performance of the heat exchanger.

It is therefore the object of the present invention to provide low-mass heat exchangers with high thermal performance. This object is achieved by a heat exchanger of the type specified at the outset, which is also designed so that the surface elements are formed like a fins projecting from the partition and the surface elements have reinforcing beads, wherein the Verstärkungswülste extend up to the partition wall. that the surface elements extend at an angle greater than zero and equal to or less than 90 ° from the dividing wall, and that the thickness of the surface elements, also referred to as wall thickness, is small relative to the surface area of the surface elements, the thickness being parallel to the dividing wall and perpendicular to the surface Preferably, the surface elements extend perpendicularly from the dividing wall The surface elements are rigidly connected to the dividing wall and likewise rigid in themselves.

The serving as ribs of the heat exchanger surface elements are divided into thin-walled surface areas with correspondingly low volume and low mass. The subdivision is done by Verstärkungswülste with larger cross sections for increased heat conduction. That is, the reinforcing beads have a greater thickness than the surface portions. The reinforcing beads are oriented to direct the heat towards or away from the partition wall between the two media, depending on how the temperature gradient passes.

The heat exchanger can be a liquid-gas heat exchanger, for example a water-air heat exchanger. The heat exchanger, may be formed as a finned tube heat exchanger, wherein the partition between the first fluid (eg water) and the second fluid (eg air) is formed through the tube wall of the tubes. The fluids water and air are to be understood as pure examples, which may also stand for other liquid and gaseous fluids. The tube inner sides may be in contact with a liquid, first fluid. The heat transfer resistance is small at this interface by the liquid state of matter of the first fluid. Accordingly, it requires on the inside of the tubes no surface enlargement. In cross-flow to a gas flow is performed, the main flow direction is perpendicular to the tube axis. The interfaces on the outside of the tubes in contact with the gaseous second fluid have a higher heat transfer resistance per unit area of the partition wall surface. In order nevertheless to achieve a small heat transfer resistance, the surface of the partition wall of the heat exchanger according to the invention is increased on at least this side by ribs in the form of the described surface elements. Such surface enlarging surface elements can be used in other inventive Heat exchangers may also be arranged on both sides of the partition wall, for example in a gas-gas heat exchanger.

The following statements relate mainly to a liquid-gas heat exchanger with only one side of the gas side enlarged surface. The fillings apply with appropriate modifications, however, for other heat exchangers with both sides enlarged surfaces of the partition, for which no embodiment is explicitly named.

Specifically, the heat exchanger according to the invention may be a finned tube heat exchanger with at least one tube for flowing a first fluid on the inside of the tube and for flowing around a second fluid on the outside of the tube, which is enlarged by surface elements, which are referred to as ribs in Rippenrohrwärmeübertragern. The surface elements or ribs are formed in a fin-like manner projecting from the tube and have reinforcing beads, wherein the reinforcing beads extend away from the tube.

The thermal conductivity of the fins of finned tubes is a material property of the material used to make the fins. For a large heat flow, a large cross-sectional area transverse to the heat conduction direction is needed.

The heat exchanger according to the invention uses fin-like surface elements as ribs, which have reinforcing beads spaced apart from one another and surface areas of small thickness between the reinforcing beads. The surface areas have a high thermal resistance due to their small thicknesses. The Verstärkungswülste, however, have a larger cross-section and a low thermal resistance, which is sufficiently small for the heat transfer over long lengths. The heat conduction in these surface elements is partially in two stages: For example, if the second fluid on the outside of the tube has a lower temperature level than the fluid on the inside of the tube, the heat conduction takes place first of the pipe wall or other partitions in the Verstärkungswülste and there in the Surface areas between the reinforcing beads. In the immediate vicinity of the pipe wall, a direct heat input from the pipe wall into the surface areas dominate, while the heat is only partially conducted to the Verstärkungswülsten. The Verstärkungswülste stand with its cross-section in contact with the pipe or the pipe wall or other partition wall and extend away from the pipe. In other words, that is the reinforcing beads orthogonal or at an angle to the tube wall, but not parallel or otherwise spaced from the tube wall.

In a round tube, the reinforcing beads may extend radially and in the case of flat partitions orthogonal to the dividing wall, so that the heat is conducted in a short distance from the dividing wall or to the dividing wall. For example, the Verstärkungswülste for geometrical or aerodynamic reasons, also run differently to the pipe. The reinforcing beads of the surface elements of the heat exchangers according to the invention may extend substantially through the entire surface element up to an outer edge of the surface element. Alternatively, the reinforcing beads may also be formed only on a partition wall-side partial surface of the surface element and terminate in front of the outer edge of the surface element remote from the partition wall. The cross-section of the reinforcing beads may also be formed towards the partition wall with increasing size. The reinforcing beads may have a circular or oval cross-sectional shapes. But there are also other cross-sectional shapes possible. The diameter of circular reinforcing beads may be at least twice as large as the thickness of surface areas between the reinforcing beads.

The reinforcing beads of adjacent surface elements can be arranged offset from one another. A fluid, for example air, flowing transversely to the reinforcing beads is deflected at the reinforcing beads. By an offset of reinforcing beads located in adjacent surface elements, a wave-shaped fluid flow can be generated. The undulating fluid flow can also be considered as a streamlined turbulence. By turbulence, an increased convective heat transfer from the surface elements and partitions to the fluid flowing around or vice versa can be achieved. The good heat conduction due to the presence of the reinforcing beads results in a relatively large temperature difference between the surface member and the medium surrounding the surface member. As a result of the large temperature difference, a large heat flow between the surface element and the surrounding medium and, as a result, a large thermal output of the heat exchanger according to the invention is achieved. Adjacent surface elements may be attached to a partition wall, for example on a pipe. However, surface elements emanating from adjacent partitions may also embrace one another like a comb.

According to one embodiment of the heat exchanger according to the invention, the tube of a Rippenrohrwärmeübertragers is designed as an oval tube, the cross section of two Semicircles and two semicircles connecting the semicircles is formed The surface elements have an oval shape and are arranged in an orthogonal plane, ie orthogonal to the tube axis. On the oval tubes, the concept of the present invention can be advantageously implemented. At the surface regions of the straight regions of the oval tube, the reinforcing beads can be positioned almost perpendicular to the flow, parallel and at a constant distance from each other. In this case, a maximized convective heat transfer between adjacent surface elements can be achieved. Due to the offset Verstärkungswülste in opposing, ie, adjacent to each other, surface elements a wave-shaped flow can be formed, which further improves the heat transfer. The length of the straight line of the oval tube cross section may be at least once as large as the diameter of its semicircle, in particular 2.5 times as large. At the large straight areas of the oval tube and the adjoining areas of the surface element advantageously large heat transfer can be achieved. For mechanical and aerodynamic reasons within the tube, the oval tube or the oval flat tube can not be formed arbitrarily flat.

The individual aspects presented embodiments of the heat exchanger according to the invention can also be combined otherwise at the discretion of a person skilled in the art, without departing from the scope of the invention presented and claimed here. Properties described one after another should not be misunderstood as an inseparable combination of features, but should be understood as an enumeration of individual features.

The present invention will be explained in more detail below with reference to figures, wherein

1 shows a heat exchanger according to the invention in a perspective view,

2 shows a fluid flow at the heat exchanger according to the invention,

Fig. 3 is a view of a Rippenrohrwärmeübertragers invention in the direction along the pipe and

Fig. 4 shows a view of the invention Rippenrohrwärmeübertragers in the direction transverse to the pipe.

Figure 1 shows a heat exchanger 1 according to the invention, specifically a finned tube heat exchanger, fragmentary in a perspective view. In the center of the illustrated object, the oval tube 2 can be seen. The walls of the tube 2 are partitions between a first fluid in the interior of the tube 2 and a second fluid outside the tube 2. Through the partition wall or the tube wall is heat between the exchanged first and the second fluid, without the first and the second fluid materially come into contact with each other. On the outside, the tube 2 has surface enlarging ribs, which give its name to the finned tube heat exchanger. In the heat exchanger 1 according to the invention shown here, the ribs connected to the tube are designed as low-volume and substantially two-dimensional surface elements 3. The surface elements 3 have in the illustrated embodiment, pin-shaped reinforcing beads 4 with a round cross-section. These reinforcing beads 4 extend from the tube 2 to the outer edge of the surface elements 3. Between the reinforcing beads 4, the surface element 3 has surface areas 5 which have a smaller thickness than the reinforcing beads 4.

Figure 2 shows a detail of the heat exchanger of Figure 1 schematically in a side view of the tube 2. The same reference numerals in the figures designate the same or similar elements. To avoid repetition, reference is made to the description of Figure 1. In FIG. 2, the flow of the second fluid outside the tube 2 is shown schematically on the basis of streamlines 6. The reinforcing beads 4 interfere with laminar flow between adjacent surface elements 3 by causing turbulence. The turbulence improves the heat transfer between the second fluid and the surface element 3. On the flat side of the oval tube 2, the reinforcing beads 4 of adjacent surface elements 3 are arranged parallel to one another. In addition, they are each in the flow direction, which runs in the representation from bottom to top, each with an offset

7 arranged to each other. Due to the offset 7, the turbulence on the one-to-one reinforcing beads 4 overlap to the streamlined wave pattern outlined with the streamlines 6.

In FIGS. 3 and 4, a very specific design example of the finned tube heat exchanger of FIGS. 1 and 2 is shown in two different views along the tube 2 and transversely thereto. The tube 2 is here designed as an oval tube, which opposes the flow shown in Figure 2 with the streamlines 6 at the same cross section a lower resistance than a round tube of the same cross-sectional size. The concrete oval tube has an outer diameter 9 of 12 millimeters of its semicircular wall sections and a length 8 of the straight side sections of 30 millimeters. For a scaling of the pipe can be generalized that the ratio of the straight length

8 to the diameter 9 is 2.5. The exact size of this ratio can be used as an optimization parameter in the design of the heat exchanger based on given conditions. In Figure 4 it can be seen that the surface areas 5 a have small thickness of only 1 millimeter and have the Verstärkungswülste 4 with a maximum thickness of 3 mm in comparison with the surface areas 5 enlarged cross-section or have three times the thickness.

It can be seen in the detail from FIG. 4 that the left surface element 3 has only three reinforcing beads 4 on the flat surface area of the oval tube 2. By contrast, the right-hand surface element 3 has four reinforcing beads 4 in the same cut-out. Due to the different number of Verstärkungswülste 4 of the offset 7 is realized and ultimately the sketched in Figure 2 flow path with the streamlines 6. Furthermore, the offset of Verstärkungswülste provides for different temperature profiles and thus large temperature differences between the fluid 2 and each surface element 3, which is why large heat flux densities are possible.

In the illustrated embodiments, the adjacent surface elements 3 are mounted on a tube 2. In other examples, not shown, adjacent surface elements 3 are mounted on adjacent tubes 2 and the fins of adjacent tubes engage in one another like a comb. Further embodiments can be derived by a person skilled in the art from the above examples in adaptation to a given task.

reference numeral

1 heat exchanger

2 pipe

3 surface element

4 reinforcing bead of the surface element

5 surface area of the surface element

6 streamlines of a fluid between adjacent

interface elements

7 Offset of reinforcing beads

8 Straight line of the oval tube

9 Diameter of the semicircle in the oval tube cross-section

Claims

claims

1 . Heat exchanger (1) having at least one partition wall and at least from one side of the partition wall and the surface of the partition wall enlarging surface elements (3), which are flowed around by a fluid, wherein the surface elements (3) are formed like a fins projecting from the partition and the surface elements (3) reinforcing beads (4) and between the Verstärkungswülsten (4) located surface areas (5), wherein the Verstärkungswülste (4) extend to the partition, characterized in that the Verstärkungswülste (4) have a circular or oval cross-sectional shape ,

2. Heat exchanger (1) according to claim 1, characterized in that the heat exchanger (1) is a finned tube heat exchanger, with at least one tube (2) for the flow of a first fluid inside the tube (2) and with the surface of the tube (2 ) surface elements (3) which increase in size and can be flowed around by a second fluid in cross-flow to the fluid 1, wherein the tube (2) forms the dividing wall of the heat exchanger (1).

3. Heat exchanger (1) according to claim 2, characterized in that the Verstärkungswülste (4) extend orthogonal to the surface of the tube (2).

4. Heat exchanger (1) according to claim 1, characterized in that the Verstärkungswülste (4) through the entire surface element (3) extend to an outer edge of the surface element (3).

5. Heat exchanger (1) according to claim 1, characterized in that the Verstärkungswülste (4) have a circular cross-section and the diameter of the reinforcing beads at least twice as large as the thickness of the surface areas (5) between the Verstärkungswülsten (4) of the surface elements ( 3).

6. Heat exchanger (1) according to claim 1, characterized in that the Verstärkungswülste (4) of adjacent surface elements (3) are offset from each other to form an offset (7) in a flow direction of the second fluid between the surface elements (3).

7. Heat exchanger (1) according to claim 2 and 6, characterized in that the tube (2) of the Rippenrohrwärmeübertragers is formed as an oval tube whose cross section of two semicircles and two semicircles connecting straight lines is formed, the surface elements (3) with a oval shape are arranged in a plane orthogonal to a longitudinal axis of the tube and

adjacent surface elements (3) are arranged parallel to each other.

8. Heat exchanger (1) according to claim 7, characterized in that the length of the straight line (8) of the cross section of the oval tube at least once as large as the diameter (9) of the semicircle of the cross section of the oval tube, in particular 2.5 times as large is.